According to data and statistics, drug-resistant strains of malaria tend to emerge in ares with low transmission but that seems to be the opposite of how we would think about it logically. And researchers might have found the answer to this puzzle. It's all in the math.

Researchers from Emory University in Georgia, US, might have cracked the puzzle – and the answer lies not in environmental or public health factors, but in sheer, brute mathematics. “It's basically a numbers game,” says lead author Mary Bushman.

In order to try to resolve the issue, she and her colleagues set up a computer model that ran simulations of malaria transmission over a period of roughly 14 years. The model contained 400 digital people who were attacked, on a random basis, by 12,000 digital mosquitoes.

The first thing that became apparent was that earlier simulations contained a serious flaw. The models had assumed that people co-infected by both strains would contain a parasite population that split evenly between the two.

“But our model showed that the system is asymmetrical,” explains Bushman. “When you put two strains in a host they virtually never split 50-50.”

And this led to a second, critical observation: the time of infection was critical.